Influence of Laval tube geometry on airflow characteristics in yarn suction gun for polyester fully drawn yarn

For the purpose of providing technique support for improvement of yarn suction gun,software CFX 12. 1 was used to simulate airflow patterns in the yarn suction gun with different geometrical parameters of the Laval tube,and the relation between the flow patterns and yarn suction performance was discussed. The influence mechanism of Laval tube geometry on the yarn performance was clarified. The simulation results and the experimental ones are in good agreement and the rational parameters were obtained as follows: the converging angle of Laval tube α = 90° and the diverging angle of Laval tubeβ = 6°. A rational converging angle of Laval tube accelerates the airflow smoothly in the Laval tube,and avoids more backflows and strong normal shock wave occurred in the Laval tube,which reduces kinetic energy loss. As a result,the suction efficiency increases. The suction efficiency can be raised through an appropriate diverging angle,which makes circumferential velocity component of airflow and air region of high speed and high density moderate. This increases drag force of air on the yarn and reduces friction of wall on the yarn and kinetic energy loss caused by the normal shock wave.